Osmoregulation and Excretion in Humans part 2 Flashcards
Normal conditions
- 1,600 L of blood flows through a pair of human kidneys each day, yielding about 180 L of initial filtrate
- Both the volume and composition of the filtrate are changed dramatically as processing occurs
- About 99% of the water and nearly all of the sugars, amino acids, vitamins, and other organic nutrients are reabsorbed
- Leaves about 1.5 L of urine to be transported to bladder
Osmosis direction
-Water diffuses from where ITS concentration is HIGH (dilute solute) to where ITS concentration is low (concentrated solute)
Osmolarity (osmotic concentration)
- The measure of solute concentration
- The number of osmoles of solute per liter of solution
- In the kidneys, we’re looking at concentrations of Na+ and Cl- as solutes
Goals of the kidneys
- Removing metabolic wastes/toxins
- Osmoregulation - salt and water balance
Initial filtration
Occurs at the filtration membrane
non-specific
Filtration occurs at filtration slits
anything small enough to fit between slits enters the nephron (glucose, amino acids, vitamins, and toxins)
-Cells and large proteins are trapped in capillaries
With normal kidney function, which is present in plasma but not in filtrate
Proteins and blood cells
What is the descending limb permeable to
Only water
What is the ascending limb permeable to
Only Na+ and Cl-
May leave nephron by passive or active transport
What does the movement of salts out of the ascending limb create?
The solute gradients
Proximal convoluted tubule (PCT)
-Closely associated with peritubular capillaries bed
Function:
- Passive and active transport (need energy for active)
- Reabsorption of water, ions, glucose, and amino acids into capillaries (co-transport with Na+)
- Secretion of nitrogenous wastes and toxins (ex. aspirin, morphine)
(Numbers in nephron indicate the osmolarity (amount of solute) in the filtrate)
Nephron loop (Loop of Henle) Main function
- Major function is to use active transport to move Na+ and Cl- into the kidney medulla
- Associated with vasa recta capillary bed
Nephron Loop (descending limb)
- Descending limb is only permeable to water
- Osmolarity of medulla increase moving away from cortex
- Water moves via osmosis through aquaporins and is reabsorbed into the blood concentrating the filtrate in nephron
Nephron Loop (ascending limb)
- Ascending limb is only permeable to ions (primarily Na+ and Cl-)
- In thin segment NaCl, which had become concentrated in descending limb, diffuses out of nephron (helps maintain high osmotic concentration)
- In thick segment, NaCl is actively transported out and filtrate becomes more dilute
Distal convoluted tubule (DCT)
- Reabsorption of water is influenced by hormones
- Secretion of any extra wastes
- Important site of proton (H+) absorption or secretion
- Works with respiratory system to balance pH
Carbon Dioxide transport
- Dissolved in blood plasma (~10%)
- Bound to hemoglobin (~20%)
- In the form of plasma bicarbonate (~70%)
- In many respects, [CO2] more important in determining respiratory rate
Homeostatic response
Include coordination between respiratory efferent pathways and urinary secretion/reabsorption of proteins
What happens if there is a problem with the DCT that prevents the secretion/absorption of protons (H+)
It can lead to metabolic acidosis or metabolic alkalosis
Associated with bicarbonate excess or deficiency
Metabolic acidosis
Too many protons
Metabolic alkalosis
Too few protons
What is the concentration of carbonic acid in the blood dependent on
The level of CO2 in the body and the amount of CO2 gas exhaled through the lungs
Carbonic acid lost and formed regarding CO2
A molecule of carbonic acid is lost for every molecule of CO2 exhaled, and a molecule of carbonic acid is formed for every molecule of CO2 retained
(The respiratory contribution to acid-base balance is usually discussed in terms of CO2 rather than of carbonic acid)
Respiratory acidosis
CO2 excess
Can result from anything that interferes with respiration, such as pneumonia, emphysema, or congestive heart failure
Respiratory alkalosis
CO2 deficiency
Occurs when too much CO2 is exhaled from the lungs, as occurs in hyperventilation
Hypercapnia
Too much carbon dioxide, increase in protons, decreases pH
Results in acidosis (acidic blood)
Hypocapnia
Too little carbon dioxide, decrease in protons, raises pH
Results in alkalosis (basic blood)
Water conservation in the collecting duct
Main function: absorb more water
Relies on the solute gradient that was created by the nephron loop (osmosis drive water to be reabsorbed from the duct)
Influenced by hormones
Steps in the kidney
1: Initial filtration
2: Reabsorption/Secretion at the PCT
3: “Salty” medulla in the Nephron Loop
4: Reabsorption/Secretion at the DCT
5: Water conservation in the collecting duct
